Effects of a Mandatory Daily Spontaneous Breathing Trial on Ventilator Weaning in a Surgical ICU
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: A year after implementation of a mandatory daily spontaneous breathing trial in all ventilated patients in the authors' surgical ICU, the proportion of patients who were extubated after passing the trial had increased from 27% to 42%, without an increase in the rate of reintubation.
Source: Robertson TE, et al. J Am Coll Surg. 2008;206:489-495.
This study from the department of surgery at Washington University School of Medicine in St Louis sought to determine the effect on extubation and reintubation rates of implementing a mandatory daily spontaneous breathing trial (SBT) in every qualifying ventilated patient and reporting its results to the physicians managing that patient. A protocol for patient assessment and performance of an SBT was established as "best practice" in the authors' surgical ICU in July 2005, and data were recorded in 8-week periods as part of a quality improvement project over the next 15 months. To assess the effects of implementing the protocol, and to account for variations in season and house staff experience, the same 8-week periods from 2005 and 2006 were compared.
The protocol for SBTs was the "common protocol for daily spontaneous-breathing trials agreed on by the Partnership for Excellence in Critical Care in Miami, FL, November 2005." It consisted of an initial safety screen for SBT appropriateness by the patient's nurse, a 2-minute initial assessment of spontaneous breathing on 5 cm H2O pressure support and 5 cm H2O positive end-expiratory pressure, carried out by the nurse and respiratory therapist, and then a 30-minute SBT on the same settings, as tolerated by the patient. All assessments were by bedside observation and monitoring, including pulse oximetry, and arterial blood gases were not a mandatory part of the protocol. Standardized assessment criteria were used to stop or continue the trial and to report its results. At the end of the trial, the results were reported to the patient's physician. The proportion of patients who were extubated within 24 hours of the SBT, and the number of subsequent reintubations, were the primary endpoints. After the first 6 months of the new protocol (and after the initial 8-week comparison data had been recorded), it was changed so that physicians were required to indicate the specific reasons for continuing ventilatory support in patients who passed the SBT.
During the 15 months of observation, 427 of 488 patients who were ventilated for > 24 h underwent SBTs. Of these, there were 73 patients in the first 8-week comparison period and 57 patients in the second period. Demographic data on these latter groups and their diagnoses were generally similar. Their mean APACHE II scores were 18.6 and 19.2, respectively. In the initial 8 weeks of the protocol, there were 35 extubations out of 131 passed SBTs (27%), whereas in the comparison period one year later, 42 of 101 passed trials resulted in extubation (42%; p < 0.02). Reintubation rates in the two periods were 6% and 8%, respectively. The median duration of ventilatory support was 5.0 days (interquartile range, 2.7-9.8) vs 2.9 days (IQR, 1.8-6.3) in the initial and subsequent 8-week periods, respectively (p < 0.02).
Commentary
This study demonstrates that implementation of a protocol involving an automatic daily SBT in appropriate mechanically ventilated patients, and reporting the results to the physicians managing those patients (plus requiring a statement of justification for not extubating patients who pass the SBT), is associated with more frequent extubation after passed SBTs, no increase in the rate of re-intubation, and a decrease in the overall duration of mechanical ventilation among patients in the unit. As just stated, these findings are consistent with those of numerous previous studies and are nothing especially new. However, I think this study shows two important things.
First, it tells us about everyday actual practice rather than what happened during the artificial clinical context of a deliberate prospective trial. For some time, international weaning guidelines have called for daily SBTs as the only way to tell whether a patient is really ready for liberation from ventilatory support.1 This recommendation was based both on the results of clinical trials of weaning protocols and on the vast and disappointing literature on predictive measurements ("weaning parameters") for determining when weaning should be attempted.2 The present study supports the notion that implementation of daily SBTs in actual practice does in fact shorten the duration of invasive mechanical ventilation, without an increase in reintubation rate.
Second, although the rate of extubation following successful SBTs improved significantly in the authors' unit during the year after the new protocol was implemented, it remained quite low. Complete data on why most of the patients who passed their SBTs remained intubated are not provided in the paper. However, a 42% extubation rate after a successful SBT is substantially lower than has been observed in clinical trials of weaning protocols. The authors make the following statement in the introduction: "In general practice, the decision to extubate is based on complex factors, some of which are related to patient disease and others related to caregiver practice patterns." This is unquestionably true, but is practice variation "related to caregiver practice patterns" justifiable when substantial variations in patient outcomes and costs are involved?
Studies have shown that delayed extubation, once patients no longer meet criteria for continued ventilatory support, is associated with prolongation of the duration of mechanical ventilation and overall ICU stay, and also with higher rates of ventilator-associated pneumonia. This is true even for brain-injured patients who are not fully awake.3,4 suggesting that "altered mental status" is not by itself a reason for delaying extubation.
In conclusion, to quote the authors, "...implementation of a protocolized SBT initiated at the bedside by nonphysician providers is safe and can result in improved extubation rates. Requesting physician documentation of reasons for continuing mechanical ventilation despite a passed SBT can be a substantial factor in increasing extubation rates and improving communication." This article documents some important steps toward reducing practice variation in mechanical ventilation, and in decreasing adverse effects associated with ventilatory support.
References
- MacIntyre NR, et al. Chest. 2001 Dec;120(6 Suppl):375S-95S.
- Pierson DJ. The role of weaning parameters in 2008. Crit Care Alert. 2008 Mar;15(12):91-95.
- Coplin WM, et al. Am J Respir Crit Care Med. 2000;161:1530-1536.
- Namen AM, et al. Am J Respir Crit Care Med. 2001 Mar;163(3 Pt 1):658-664.
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